An object placed 45cm from a lens forms an image on a screen place 90cm on the other side of the lens. Identify the type of the lens and find its focal length.
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Given, Object distance, u=-45 cm Image distance, v= 90 cm Focal length, f=? By lens formula;$\frac{1}{\text{f}}=\frac{1}{\text{v}}-\frac{1}{\text{u}}$
$\frac{1}{\text{f}}=\Big[\frac{1}{90}\Big]-\Big[-\frac{1}{45}\Big]$
$\text{f}=30\text{cm}$
Since the focal length is positive, therefore the lens is convex lens of focal length 30cm.
$\frac{1}{\text{f}}=\Big[\frac{1}{90}\Big]-\Big[-\frac{1}{45}\Big]$
$\text{f}=30\text{cm}$
Since the focal length is positive, therefore the lens is convex lens of focal length 30cm.
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